1. Field of the Invention
The present invention relates to a biochemical measuring device configured to measure a concentration of a specific substance contained in measured sample solution including electrolyte and, more specifically, to a biochemical measuring device configured to be capable of reducing a waiting time when measuring a concentration of a specific substance continuously.
2. Description of the Related Art
In the related art, a biochemical measuring device configured to measure a concentration of a specific substance contained in measured sample solution is used. As one of biochemical measuring devices, JP-A-9-397120 discloses a urine glucose meter configured to measure a specific substance contained in urine as measured sample solution, that is, a urine glucose value (glucose concentration) by a glucose sensor as a current detecting-type chemical sensor. For example, a two-electrode type glucose sensor includes a pair of conductive electrodes (a working electrode and a counter electrode) arranged on an insulative substrate, and an enzyme (glucose oxidase) film is formed on the conductive electrodes.
The glucose sensor is subject to chemical reaction in the measured sample solution as follows. By the action of the glucose oxidase, glucose in the measured sample solution is oxidized, oxygen is reduced to hydrogen peroxide, so that gluconolactone and hydrogen peroxide are generated. At this time, by an application of a voltage to the electrodes (the working electrode and the counter electrode), oxidizing reaction of the hydrogen peroxide is generated on the working electrode, thereby generating electrons and an oxidation current flows from the working electrode to the counter electrode, and the flowed oxidation current is measured as an oxidation current value. Since the amount of generation of the hydrogen peroxide is proportional to the amount of glucose, if the oxidation current value of the hydrogen peroxide is known, the concentration of urine glucose (glucose) can be measured.
Therefore, when measuring the urine glucose value using the urine glucose meter, the urine glucose concentration is measured on the basis of a difference between a base current value of a base current flowed by an application of a constant potential to a point between both electrodes (the working electrode and the counter electrode) in a state of being immersed in preservative solution which does not contain the urine glucose and a peak current value of an oxidation current flowing between the both electrodes by the application of a constant potential between the both electrodes (the working electrode and the counter electrode) in the measured sample solution.
However when a predetermined potential is applied to a point between the pair of electrodes, a charge is accumulated on a surfaces of the respective electrodes by the formation of an electric bilayer. In order to eliminate the influence of the electronic bilayer, when the urine glucose value is measured continuously by the urine glucose meter, it is required to wait for a waiting time from the termination of previous measurement and subsequent immersion of electrodes of the urine glucose meter in the preservative solution until the restoration of the base current value to a stationary current value which indicates a urine glucose concentration of zero (for example, 3 minutes) has elapsed before restarting the measurement with the urine glucose meter. Consequently, when there are a plurality of types of measured sample solution to be measured or the first measurement of the urine glucose value is failed, it is required to wait until the elapse of the waiting time before restarting the measurement.